The subject invention relates to a noninverting logic circuit, particularly suitable for one propagation delay complex logic gates, that is compatible with depletion-mode Schottky barrier field effect transistor (MESFET) inverting logic circuits. The large variety of one propagation delay complex logic gate types that can be made with the subject invention may be used in digital technology to increase the speed of operation of microprocessor type circuits and the like.
The history of integrated semiconductor circuit design has been characterized by a trend toward increasing speed and circuit densities. Various technologies have been invented to stimulate this trend. For example, transistor-transistor logic (TTL), was standard in digital equipment for a long time but has given way in many areas to N-channel metal oxide semiconductor (MOS) logic circuits because of their superiority in speed power product, packing density and ease of device fabrication. For these reasons, devices fabricated using these technologies are finding application primarily in memory, microprocessor, logic circuits, and the like. The Schottky barrier field effect transistor (MESFET) is another device that offers many of the advantages of the N-channel metal oxide semiconductor (MOS) technology without some of its disadvantages. Its primary application will also be in digital technology, such as memory circuits, random logic circuits, microprocessor type circuits and the like.
One of the major problems associated with MOSFET and MESFET technology, however, is the lack of noninverting logic circuits which provide only a one propagation delay switching speed. This is a very serious problem for it severely limits the number of complex logic gate types in which MESFET, and MOSFET, semiconductor devices can be used.
Speed is one of the principal features of merit in any logic circuit. The term "speed" usually implies the speed at which the output changes from one state to another, i.e., the slope of the transition of the output,; the delay in propagating a changed logic level through the circuit; and the rate at which the circuit can be cycled between the states, i.e., the repetition rate.
As a general principal, a semiconductor device, such as a transistor, a diode, and the like, will offer some delay in the speed at which the devices' output signal changes from one state to another in response to the devices input signal; i.e., the output signal will occur sometime after the input signal. Of course, every logic circuit, which comprises a number of circuit elements, including semiconductor devices, will, therefore, also have some delay. This delay is generally known in the art as "propagation delay time", "delay time", or simply as "delay". Many logic circuit design failures, or design limitations, result from such undesired "delay"; for the speed at which an integrated circuit can perform a logic function is inversely proportional to the propagation delay of each circuit element, including the semiconductor devices in the integrated circuit. In other words, the shorter the propagation delay of the integrated circuit, the faster is its operational "speed".
In the world of digital technology, there is a very strong demand for faster and faster operational "speeds". Accordingly, considerable effort has been devoted toward the development of complex logic gates having minimal "delay".
High-speed general purpose MESFET, and MOSFET, logic gate circuits capable of implementing two levels of logic --the "NAND" and "NOR"--in about one propagation delay have been reduced to practice. However, high speed general purpose MESFET (and MOSFET) logic gate circuits capable of implementing the two "noninverting" levels of logic --"AND" and "OR"--in only one propagation delay do not exist in the prior art.
It is a principal object of the invention to provide a noninverting circuit for one propagation delay complex logic gates that is compatible with all field effect transistor (FET), including depletion-mode Schottky barrier field effect transistor (MESFET), inverting logic circuits. Another object is to provide noninverted amplification of the input voltage signals to the circuit of the invention. An additional object is to provide a novel noninverting amplifier circuit for one propagation delay high-speed general purpose MESFET complex logic gates that is capable of implementing the two "noninverting" levels of logic --the "AND" and "OR". A further object is to provide a novel noninverting amplifier circuit for one propagation delay high-speed general purpose MOSFET complex logic gates that is capable of implementing the two "noninverting" levels of logic --the "AND" and "OR".